(1) Field of the Invention
The present invention relates to mobile communication end devices, and more specifically to a wireless communication end device used in carried state by a user, where a cell is used as an electric power source of a communication end device of mobile wireless communication system, a cordless telephone or the like.
(2) Description of the Prior Art
Mobile wireless communication system is constituted by a base station and a mobile wireless communication end device performing wireless communication with the base station. In a mobile wireless communication end device carried by a user, a cell is mainly used as its electric power source so as to make it more portable. Therefore in a mobile wireless communication end device similar to other electronic device driven by a cell, continuity is dependent on life of the cell.
Also a cordless telephone spreads widely in society because of simplicity that it may be used in any talking station, but since a part called a child device or a handset in general is carried by a user, a cell is used in its electric power source. Consequently, continuity of a cordless telephone similar to that of a mobile wireless communication end device is dependent on life of the cell.
On the other hand, in order to deal with consumption of an electric power source of an electronic device driven by a cell, such as an electronic calculator, a television or the like, for example, as disclosed in Japanese Patent Laid-Open No. 61-262826, such measure is known that voltage of a cell is observed and when the voltage falls, consumed power of the device is reduced in comparison with normal state.
With the spread of a mobile wireless communication end device or a handset, its use methods are various and regarding a use method also when power of a cell is consumed, a flexible method reflecting intention of a user is desired. Under environment where cell exchange or charging is easy, in most cases, even if the cell is consumed, it is desired that use is continuous normally without deteriorating performance. Under environment where a cell or substitute communication means is not available easily, even if the cell is consumed, it is desired that minimum required performance, for example, transmission performance be maintained as long as possible.
In the invention in Japanese Patent Laid-Open No. 61-262826 as above described, however, the main point is put on extension of the cell only and any means of reflecting the intention of the user regarding use method at consumption state of the cell is not mentioned. Also lowering of operation frequency is mentioned as means for reducing the consumed power and it cannot be applied intact to communication system which must be operated in a definite frequency.